Pentax-DA* 55mm F1.4 Review

Autofocus

The Pentax DA* 55mm does not use the camera screw drive to autofocus; the lens uses an internal SDM motor. There has been a lot of discussion on our forum about SDM failures. Recently, a survey was completed to try to get some real world evidence, rather than just anecdotal evidence. In general, the survey concluded that the failure rate of the 55mm's SDM is very low, but not entirely negligible. If you are interested in additional information, the link to the survey is here.

The SDM drive is very quiet and its major selling point (from a marketing standpoint) has been its increased speed over the camera screw drive. For this test, we decided that we would compare it to the other 50mm from the 50mm Prime Lens Shootout. The lens was timed for its response time from minimum focus distance to infinity and infinity to minimum focus distance. The test was completed three times and the times were averaged to minimize errors. Although this not a comparative review between the DA* 55mm and the DA and FA 50mm lens, we thought it would be helpful to compare the autofocus times of the three lenses. The results were then charted as seen below.

Verdict

When we did the math, the FA 50mm F1.4 had the fastest overall focusing time of the three lenses by one-tenth of a second (.1s), and the DA* 55mm F1.4 came in second. An interesting result of our tests was that the 55mm's SDM is not faster than the internal screw-drive of the K5, and that the SDM is subject to a great deal of latency. Thanks to the DA* 55mm's slightly shorter throw, the minimum focus distance to/from infinity show very similar times (we started the measurements once both motors had started moving).  On the whole, the DA* 55mm's autofocus does an acceptable job, but we do wish that it could have a faster response time.  Considering how little latency the DC autofocus system in the Pentax 18-135mm has, and how responsive it felt, we did expect more from the DA* 55mm than we got.